Tris(nonylphenyl) phosphite (TNPP) has been used for years to stabilize polymers, especially synthetic rubber products against oxidation and color degradation. The use of phosphites as stabilizer for synthetic rubbers requires that they be usually incorporated into an aqueous synthetic rubber latex prior to flocculation and drying. This means that the phosphite should have good hydrolytic stability for treating these emulsions. Tris(nonylphenyl) phosphite (TNPP) has been a standard phosphite that has been used for this application. Phosphites of this type function as stabilizers for polymers and especially synthetic rubbers by reacting with hydroperoxides forming a phosphate and a corresponding alcohol. The reduction of the peroxides slows crosslinking and color degradation. Unfortunately, organic triphosphites also hydrolyze quite readily by reacting with moisture to form a dialkyl or diaryl hydrogen phosphite. The di-substituted phosphites are not as active as tri-phosphites in decomposing hydroperoxides. Therefore, it is desirable to have a hydrolytically stable organic triphosphite so it can function over a longer period of time.
Tris(nonylphenyl) phosphite (TNPP) has been made more hydrolytically stable by the addition of amines such as tris(isopropanol) amine (TiPA). Both tris(nonylphenyl) phosphite and tris(isopropanol) amine are FDA sanctioned for use in many polymer applications. However, this is a non-satisfactory solution since the amine additive is effective only for a short period of time, and cannot be used for some purposes, such as for example, in a stabilizer composition for polyvinyl chloride (PVC) which may come in contact with food.
It has also been found that the presence of excess nonylphenol from the synthesis of tris(nonylphenyl) phosphite used to stabilize a polymer, may contribute to some color degradation. The excess nonylphenol is also volatile and has a tendency to form a sticky substance on drying equipment and processing equipment. Another very recent cause for concern regarding the presence of excess nonylphenol is the fact that it has been implicated as an estrogen mimic. Based on all of these facts, it would be very desirable to produce a pure tris(nonylphenyl) phosphite which has a low acid number, low residual chloride content and a very low level of free nonylphenol.
Tris(nonylphenyl) phosphite (TNPP) is typically produced by reacting phosphorus trichloride with an excess of nonylphenol, typically from 2-6% by weight excess nonylphenol. The reaction is left to proceed until a low acid number is obtained. Faster reaction times and lower acid numbers are obtained if a large excess of nonylphenol is used, such as &gt;5% excess nonylphenol. If a lower percentage of nonylphenol is used, e.g., &lt;4%, the reaction time to produce a low acid number is very long and typically a high chloride product is obtained. A high chloride product is undesirable due to the corrosive nature of chloride on processing equipment for polymers. Also, a high chloride content, typically results in poor hydrolytic stability. So the compromise is to have sufficient nonylphenol to force the reaction to completion thereby achieving low chloride and low acid numbers, but also within a reasonable reaction time.